Catheters are tubular medical devices which, when inserted into canals, vessels, passageways and the like of a human or animal, permit injection or withdrawal of fluids. In several applications, such as parenteral nutrition, cancer chemotherapy, and frequent antibiotic therapy, the tip of the catheter is typically positioned in areas of high volume blood flow, such as the superior vena cava, to avoid damage to the lining along the blood pathway. During insertion, the catheter may be guided into a wrong passage before it reaches its desired position. In the case of long-term use, it is possible that the catheter may be dislocated from its original position, such as when a patient sneezes. As a result of these occurrences, it is desirable for the caregiver to be able to determine the location of the catheter during initial placement, and at one or more times after placement. This is especially true in the case where the catheter is being placed near vital organs, such as the heart, lungs, and brain.
The caregiver, however, cannot see the catheter once it is implanted within the patient's body. Accordingly, systems and methods for determining the location of the tip of a catheter within a patient's body have been provided. One conventional catheter placement procedure is fluoroscopy, which uses x-ray film. This procedure, however, has many drawbacks. One drawback to this procedure is that the patient and caregivers are exposed to irradiation. In the case of the caregivers, such exposure is often continuous. Another drawback to this procedure is that it is not always accurate. By the time the x-ray is taken, developed and returned, the catheter may have moved. This procedure also requires expensive and bulky equipment that must be operated by trained personnel. In light of the heightened awareness by health care providers to reduce costs, such requirements are undesirable. Yet another disadvantage with this procedure is that it must be performed in the operating room, rather than in a more accessible and convenient doctor's office or examining room.
Another method and device for detecting the tip of a catheter is disclosed in U.S. Pat. No. 4,905,698 to Strohl, Jr. et al. In general, Strohl discloses the use of a source which generates an alternating magnetic field, a detector positioned proximate the distal end of the catheter, and a monitor to which the source and detector are connected. The detector consists of a ferrous core and a pair of leads that are wrapped around the core and fed through the lumen of the catheter to a power source. This method of detection involves phase changes of the induced detector current. By also referencing anatomical landmarks, the caregiver can determine the location of the detector, and thus the tip of the catheter. Once the tip of the catheter is properly positioned, the detector may be removed.
U.S. Pat. No. 4,173,228 to Van Steenwyk et al. also discloses a method and device for detecting the tip of a catheter. Van Steenwyk uses signal intensity to determine the catheter location.
While the Strohl and Van Steenwyk procedures eliminate the need for unnecessary exposure to radiation, they introduce other concerns. The systems disclosed by Strohl and Van Steenwyk are active systems. The detector leads are quite fragile and subject to breakage if not handled with care. The amount of power which can be safely generated within the body is limited. Also, because the detector is in contact with blood or fluids in the body, it must be biologically insulated so that it does not corrode and so that it is not damaged while within the patient's body. The Strohl and Van Steenwyk procedures are not designed for confirming the location of a catheter or other device after placement, thereby limiting its functionality, especially in the case of long-term use.
Thus, a need exists for providing systems and methods of determining the location of an implantable device within the body of a patient which address the concerns of the prior art, such as eliminating the hazards of radiation exposure and the high costs associated with fluoroscopy, eliminating the disadvantages associated with active systems, and/or determining the location of the implantable device on demand.